1. Field of the Invention
This invention relates to a magnesia-calcia clinker having a high density, and a process for its production.
2. Description of the Prior Art
As the converter operating conditions have become severer in recent years with the employment of the pure oxygen bottom-blowing system in place of LD Process, the conventional magnesia-calcia (CaO-MgO) brick for refractories has rapidly been superseded by a magnesia-carbon (MgO-C) brick. Recently, a combined blowing method comprising a combination of the pure oxygen top-blow and bottom-blow methods came into acceptance, and the operating conditions have become much severer as reflected, for example, by the higher operating temperature.
The severer operating conditions weaken the matrix portion of the MgO-C brick presumably because they induce the reaction of MgO with C to reduce MgO. The development of furnace materials of the magnesia-calcia-carbon (MgO-CaO-C) type has now been under way in an attempt to provide a high-quality brick which can replace the MgO-C type brick, but no MgO-CaO-C brick of sufficiently high quality has yet been developed.
Previously known CaO-MgO clinkers for use in the production of the MgO-CaO-C type brick included a clinker of naturally occurring dolomite obtained by calcining dolomite ore, and a synthetic magnesia-enriched dolomite clinker produced by adding lime or lime milk to magnesium hydroxide [Mg(OH).sub.2 ] obtained by the sea water-lime method, adjusting the MgO content, and calcining it. The naturally occurring dolomite clinker and the synthetic magnesia-enriched dolomite clinker both contain low-melting minerals of the MgO, CaO or SiO.sub.2 type or the CaO, Fe.sub.2 O.sub.3, Al.sub.2 O.sub.3 type distributed in the matrix portion. The low-melting minerals are formed by the reaction during the calcination of a flux source such as SiO.sub.2, Fe.sub.2 O.sub.3 or Al.sub.2 O.sub.3 added to the uncalcined dolomite or a mixture of Mg(OH).sub.2 and Ca(OH).sub.2 for the purpose of increasing the hydration resistance of the clinker. The low-melting minerals improve the hydration resistance of the clinker, but have the defect of reducing the thermal properties and slag corrosion resistance of the clinker. Accordingly, if a MgO-CaO-C brick produced from the aforesaid naturally occurring dolomite clinker or synthetic magnesia-enriched clinker is used as a lining refractory of the converter under the present-day rigorous converter operating conditions, it is unsatisfactory in regard to thermal properties, slag corrosion resistance, etc.
With the above-mentioned background, the production of a highly pure magnesia-calcia clinker with a low impurity content has aroused interest, and attempts have in fact been made to produce a highly pure magnesia-calcia type refractory by using high-purity, high-density magnesia or electrically fused magnesia as a magnesia source and high-purity electrically fused calcia as a calcia source and mixing them in accordance with a suitable particle size distribution. The resulting high-purity magnesia-calcia type refractory, however, is said to have the defect of peeling because the distribution of MgO and CaO is non-uniform.